1. Field of the Invention
The invention is based on a vane pump.
2. Description of the Prior Art
A vane pump of this kind is known from DE 199 52 167 A1. This vane pump has a pump housing that contains a rotor, which is rotatably driven by a drive shaft. The rotor has a plurality of grooves distributed over its circumference that extend at least essentially radially in relation to the rotation axis of the rotor, with a vane-shaped delivery element guided in each groove in sliding fashion. The pump housing has a circumference wall encompassing the rotor, eccentric to the rotor's rotation axis, against which the radially outer ends of the vanes rest. The pump housing has housing end walls that adjoin the rotor in the direction of its rotation axis. Due to the eccentric arrangement of the circumference wall as the rotor rotates, expanding and contracting chambers are formed between the vanes and by means of a pressure increase, the medium to be supplied is fed from a suction region to a pressure region that is offset from it in the circumference direction. As the rotor rotates, centrifugal force holds the vanes in contact with the circumference wall; but when the vane pump is being started, at low rotation speed, only slight centrifugal forces are exerted so that the vane pump only delivers a small quantity. In the known vane pump, another feed pump that forms a combined pump apparatus with the vane pump supplies compressed medium into the internal regions delimited by the vanes in the grooves of the rotor, which causes the vanes to be pressed radially outward toward the circumference wall in addition to the centrifugal force. In this case, at least one housing end wall contains an annular groove, which extends over part of the circumference of the rotor and is supplied with compressed medium by the additional feed pump. Manufacturing the annular groove in the housing end wall in this case is complex and usually has to be carried out by means of a material-removing machining process such as milling.